Steam_turbines General

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Steam Turbines and Boilers


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Steam Turbines for Marine Propulsion

http://www.brighthubengineering.com/marine-engines-machinery/55877-

steam-turbines-for-marine-propulsion/

http://www.machineryspaces.com/boiler.html

Video: https://www.youtube.com/watch?v=qqe43wSDfiw
http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.machineryspaces.com/boiler.htmlhttps://www.youtube.com/watch?v=qqe43wSDfiwhttps://www.youtube.com/watch?v=qqe43wSDfiwhttp://www.machineryspaces.com/boiler.htmlhttp://www.machineryspaces.com/boiler.htmlhttp://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/http://www.brighthubengineering.com/marine-engines-machinery/55877-steam-turbines-for-marine-propulsion/


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Marine steam turbine engines have largely been replaced bythe more economical marine two stroke diesel engine,

mainly for commercial reasons as the diesel engine is much

more economical. Notwithstanding this there are still a few

about, running like clockwork- their one big selling pointalong with reliability, little maintenance, and high speed-

pushing large cruisers and battleships along at forty knots,

but they are very thirsty. Let's find out how steam turbines

work in the context of marine turbine engines.
http://www.brighthubengineering.com/marine-engines-machinery/53537-main-engine-layout-familiarization-b-and-w-engine-room-layout/http://www.brighthubengineering.com/marine-engines-machinery/53537-main-engine-layout-familiarization-b-and-w-engine-room-layout/


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The Cross Compound Double

Reduction Turbine

For marine applications, the cross compound double reductionsteam turbine was a popular choice because it was more compact,taking up less space in the ships engine-room. It also had theadvantage of a built-in astern turbine giving easier asternmovement, with up to 50% astern output power as that of the

ahead turbine.

This was a big advantage when the first oil super tankers werebuiltthey took half a mile to stop from full ahead!

In operation, the steam is supplied from the ship's boiler as high

pressure, high temperature superheated steam and passes into thehigh pressure turbine, (HP) expanding through the blades andexiting into the low pressure turbine through a large boreinsulated pipe.
http://www.brighthubengineering.com/marine-engines-machinery/31422-a-tour-inside-the-engine-room-of-a-ship/http://img.bhs4.com/86/0/860bd8a0fbb4d4c2125579d8a667d7710e8442f1_large.jpghttp://img.bhs4.com/86/0/860bd8a0fbb4d4c2125579d8a667d7710e8442f1_large.jpghttp://www.brighthubengineering.com/marine-engines-machinery/31422-a-tour-inside-the-engine-room-of-a-ship/http://www.brighthubengineering.com/marine-engines-machinery/31422-a-tour-inside-the-engine-room-of-a-ship/http://www.brighthubengineering.com/marine-engines-machinery/31422-a-tour-inside-the-engine-room-of-a-ship/


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From here the low pressure steam passes through LP turbine blades,exiting from these and then being drawn by vacuum from the last fewstages into main condenser.

The high pressure and low pressure turbines are really separate turbineshaving their own drive shafts, which are coupled to a double reductiongearbox that decreases their revolutions from several thousand to about100 RPM, the normal operating propeller shaft speed.

The high pressure turbine rotor also has several rows of blades that areused as an astern turbine, which enables the ship to maneuver whenarriving or departing ports. Also the astern turbine can be used in anemergency to avoid collision at sea, and although I have had to

emergency stop and put astern a large marine main diesel engine, I havethankfully never had to carry this operation out on any steamships that Iserved on as marine engineer, as they were all tankers, so I cannotcomment on its viability.


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Both the high pressure and low pressure steam turbines haveglands at each end which stop the steam from escaping into

the engine-room from the high pressure stage and which stop

the loss of condenser vacuum through the low pressure stage.

These glands are known as labyrinth type and, as the namesuggests, are made up of a series of three rings and are

supplied with two different pressures, which effectively seals

both turbines shafts and end covers, with the supplied steam

exiting to the gland cooler.


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A common lube oil system is used to lubricate the variouscomponents and keep them cool by pumping the oil through acooler. The oil is drawn from the drain tank a through a set ofmagnetic strainers by the lube oil pump into a set of duplex filters,then onto the main lube oil cooler before supplying oil under

pressure to the turbine white metal bearings, gearbox, gearboxsprays, and thrust block. There is also a secondary back-up lube oilpump driven by the turbine shaft supplying oil to gearbox andthrust.

An overhead tank, usually positioned at the top of the engine-room, is also supplied by the pump through a bleed off orifice.From the tank there is a vertical overflow pipe incorporating acircular glass window, usually illuminated from behind, fromwhich the oil can be observed flowing back down into the system.


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The reason for the header tank is in the event of a black-outor loss of a lube-oil pump, the header tank has the capacity to

keep the turbine bearings supplied with oil until the turbine

stops rotating, with the auxiliaries being supplied by the

secondary pump. It is usual to have a lube oil purifier orcentrifuge located within the system to remove any ingress of

water or impurities from the oil.

There is also another lube oil system known as gravity feed

whereby the lubrication of all the components is by theoverhead tank; this system is shown in the sketch.


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Warming Through After the turbines and steam supply/exhaust have being idle in port,

about two hours before standby, the turning gear should be withdrawnand the steam supply and exhaust system slowly warmed through. This iscarried out firstly by raising a full vacuum about 28-29 Hg, and oncethis has been achieved, the ahead steam valve should be slowlyopened afew notches rotating the shaft a few revs only, holding for one minutebefore shutting again, the astern turbine also being operated similarly.This should be continued to ensure all the pipe-work, turbine covers androtors, expansion plates and condensate returns to boilers are all wellwarmed through and expanded up to working temperature.

Remember any water in the system will damage the turbines so onlysuperheated steam should be used, and operate the steam drains andcheck the steam traps if applicable

A typical steam turbine layout in a ship's engine room is shown below.


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Steam turbines and gearing operating

principle

http://www.machineryspaces.com/steam-turbines.html


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The steam turbine has until recently been the first choice forvery large power marine propulsion units. Its advantages of

little or no vibration, low weight, minimal space

requirements and low maintenance costs are considerable.

Furthermore a turbine can be provided for any power rating

likely to be required for marine propulsion. However, the

higher specific fuel consumption when compared with a

diesel engine offsets these advantages, although refinements

such as reheat have narrowed the gap.


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Fig: Energy conversion in a steam turbine


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The steam turbine is a device for obtaining mechanical workfrom the energy stored in steam. Steam enters the turbine

with a high energy content and leaves after giving up most of

it. The high-pressure steam from the boiler is expanded in

nozzles to create a high-velocity jet of steam. The nozzle actsto convert heat energy in the steam into kinetic energy. This

jet is directed into blades mounted on the periphery of a

wheel or disc (Figure above).


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The steam does not 'blow the wheel around'. The shaping of theblades causes a change in direction and hence velocity of the steamjet. Now a change in velocity for a given mass flow of steam willproduce a force which acts to turn the turbine wheel, i.e. massflow of steam (kg/s) x change in velocity (m/s) = force

(kgm/s2).

This is the operating principle of all steam turbines, although thearrangements may vary considerably. The steam from the first setof blades then passes to another set of nozzles and then blades andso on along the rotor shaft until it is finally exhausted. Each setcomprising nozzle and blades is called a stage.


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Steam Turbines Warming Through

The turbines are to be warmed through gradually following a stay in port or other occasion whenthey have been shut down. The bulkhead, stop, and manoeuvring valves are to remain shut.Warming through is to commence, not less than 12 hours prior to the estimated time of departure.The Deck Officer of the watch, or Duty Deck Officer is to be contacted and permission to turn theturbines/propeller requested.

Once the Deck Officer has confirmed that this can safely be carried out then and only then can theturbines be turned.

Lubricating oil circulation is to be started, and low vacuum created. Rotation can then commenceafter which the gland steam can be opened gradually. On no account is gland steam to be admittedwith the turbine rotors stationary. The temperatures are to be raised to the manufacturersrecommendations. Once this has been achieved the turning gear can be disengaged.

It is the responsibility of the Chief Engineer Officer to ensure that disengagement of the turninggear is physically sighted. No reliance is to be placed on any remote indicating devices. A request isthen to be made to the Officer of the watch on the bridge for permission to turn the engine on livesteam.


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Normal Operation

The main engine is to be operated within the limits of power,

maximum evaporative capacity and pressure of the boilers,

and the revolutions per min set out in the commissioningletter issued when the vessel entered Company service.

Only if subsequent specific instructions have been issued by

the Company, are the original commissioning letterparameters to be countermanded.


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Stand By Manoeuvring

The Officer of the watch on the Bridge must give the EngineDepartment at least one hours notice before Stand By formanoeuvring. Regardless of the time of day or type of vessel i.e.

unmanned engine room or conventional watchkeeping, the ChiefEngineer Officer, and the Engineer Officer of the watch or DutyEngineer Officer are to be informed.

Reduction in speed from full speed to the recognised manoeuvringspeed is to be as gradual as possible and in accordance with themanufacturers instructions. The operating parameters are to bemaintained avoiding sudden variations of boiler loading etc.


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Cooling Down

When the main turbines are stopped and "Finished with Engines"has been rung, the nozzle control, manoeuvring, guardian,

bulkhead and stop valves are to be shut and verified as shut. As

soon as the above mentioned valves are verified as shut,permission is to be sought from the Officer of the watch on theBridge to turn the turbines/propeller.

Once permission is granted, then the turning gear is to be engagedand the turbines rotated with the lubricating oil supply

maintained, low vacuum, and gland steam on, over a minimumperiod of 4 hours.


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Maintaining Temperatures during Short Stays inPort

If the ETD is six hours or less then the following procedure is

to be adhered to. Following "Finished with Engines"permission is to be sought to turn the turbines/propeller onlive steam. With the lubricating oil supply maintained, lowvacuum, and gland steam on the turbines are to be turned onahead steam for approximately 2 propeller revolutions every

five minutes, using astern steam as appropriate for checkingahead rotation only.


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Control Systems Maintenance

Testing and maintenance of any turbine control system alongside aberth is strictly forbidden under live steam conditions. The mainsteam stop, guardian and bulkhead stop valves are to be shut prior

to maintenance work being carried out.

In the case where a simulated test would be unsatisfactory andoperation with live steam has to be carried out, then the vessel isto be suitably anchored or stopped at sea, before maintenance or

testing is carried out. Running Hours for Turbines and Boilersshould be recorded in the Turbine and Boilers Running Hoursand returned to the Managing Office on a monthly basi


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Turbine protection

A turbine protection system is provided with all installations to prevent damage resulting from an internal turbinefault or the malfunction of some associated equipment. Arrangements are made in the system to shut the turbinedown using an emergency stop and solenoid valve. Operation of this device cuts off the hydraulic oil supply to themanoeuvring valve and thus shuts off steam to the turbine. This main trip relay is operated by a number of mainfault conditions which are;

1. Low lubricating oil pressure.2. Overspeed.3. Low condenser vacuum.

4. Emergency stop.5. High condensate level in condenser.6. High or low boiler water level.Other fault conditions which must be monitored and form part of a total protection system are:

1. HP and LP rotor eccentricity or vibration.2. HP and LP turbine differential expansion, i.e. rotor with respect to casing.3. HP and LP thrust bearing weardown.4. Main thrust bearing weardown.

5. Turning gear engaged (this would prevent starting of the turbine).

Such 'turbovisory' systems, as they may be called, operate in two ways. If a tendency towards a dangerouscondition is detected a first stage alarm is given. This will enable corrective action to be taken and the turbine isnot shut down. If corrective action is not rapid, is unsuccessful, or a main fault condition quickly arises, the secondstage alarm is given and the main trip relay is operated to stop the turbine.


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Steam turbines gearing arrangement

Turbine gearing

Steam turbines operate at speeds up to 6000rev/min.Medium-speed diesel engines operate up to about

750rev/min. The best propeller speed for efficient operationis in the region of 80 to l00 rev/min. The turbine or engineshaft speed is reduced to that of the propeller by the use of asystem of gearing. Helical gears have been used for manyyears and remain a part of most systems of gearing. Epicyclic

gears with their compact, lightweight, construction are beingincreasingly used in marine transmissions.


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Epicyclic gearing

This is a system of gears where one or more wheels travel

around the outside or inside of another wheel whose axis is

fixed. The different arrangements are known as planetary

gear, solar gear and star gear The wheel on the principal axis is called the sun wheel. The

wheel whose centre revolves around the principal axis is the

planet wheel. An internal-teeth gear which meshes with the

planet wheel is called the annulus.

Fig: Steam turbine epicyclic gearing


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Fig: Steam turbine epicyclic gearing


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The different arrangements of fixed arms and sizing of thesun and planet wheels provide a variety of different reduction

ratios. Steam turbine gearing may be double or triple

reduction and will be a combination from input to output of

star and planetary modes in conjunction with helical gearing(Figure below).


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The different arrangements of fixed arms and sizing of thesun and planet wheels provide a variety of different reduction

ratios. Steam turbine gearing may be double or triple

reduction and will be a combination from input to output of

star and planetary modes in conjunction with helical gearing(Figure below).


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Fig: Turbine reduction gear


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Helical gearing

Single or double reduction systems may be used, although

double reduction is more usual. With single reduction the

turbine drives a pinion with a small number of teeth and this

pinion drives the main wheel which is directly coupled to thepropeller shaft. With double reduction the turbine drives a

primary pinion which drives a primary wheel. The primary

wheel drives, on the same shaft, a secondary pinion which

drives the main wheel. The main wheel is directly coupled tothe propeller shaft. A double reduction gearing system is

shown in Figure below.


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Fig: Turbine double reduction system


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All modern marine gearing is of the double helical type. Helicalmeans that the teeth form part of a helix on the periphery of thepinion or gear wheel. This means that at any time several teeth arein contact and thus the spread and transfer of load is muchsmoother. Double helical refers to the use of two wheels orpinions on each shaft with the teeth cut in opposite directions. Thisis because a single set of meshing helical teeth would produce asideways force, moving the gears out of alignment. The double setin effect balances out this sideways force. The gearing systemshown in Figure is double helical.

Lubrication of the meshing teeth is from the turbine lubricating oilsupply. Sprayers are used to project oil at the meshing points bothabove and below and are arranged along the length of the gearwheel.


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Flexible coupling

A flexible coupling is always fitted between the turbine rotor and the gearboxpinion. It permits slight rotor and pinion misalignment as well as allowing foraxial movement of the rotor due to expansion. Various designs of flexiblecoupling are in use using teeth, flexible discs, membranes, etc.

The membrane-type flexible coupling shown in Figure above is made up of atorque tube, membranes and adaptor plates. The torque tube fits between theturbine rotor and the gearbox pinion. The adaptor plates are spigoted anddowelled onto the turbine and pinion flanges and the membrane plates are

bolted between the torque tube and the adaptor plates. The flexing of themembrane plates enables axial and transverse movement to take place. Thetorque tube enters the adaptor plate with a clearance which will provide anemergency centring should the membranes fail. The bolts in their clearanceholes would provide the continuing drive until the shaft could be stopped.


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Fig: Turbine flexible coupling


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Turning gear

The turning gear on a turbine installation is a reversibleelectric motor driving a gearwheel which meshes into the

high-pressure turbine primary pinion. It is used for

gearwheel and turbine rotation during maintenance or when

warming-through prior to manoeuvring.


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Part II.

Marine Boilers


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Boilers

Boiler arrangement for general cargo ships - how it works ?

http://www.machineryspaces.com/boiler.html
http://www.machineryspaces.com/boiler.htmlhttp://www.machineryspaces.com/boiler.htmlhttp://www.machineryspaces.com/boiler.html


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A boiler in one form or another will be found on every type of ship.Where the main machinery is steam powered, one or more largewatertube boilers will be fitted to produce steam at very hightemperatures and pressures. On a diesel main machinery vessel, asmaller (usually firetube type) boiler will be fitted to provide steam forthe various ship services. Even within the two basic design types,

watertube and firetube, a variety of designs and variations exist.

A boiler is used to heat feed water in order to produce steam. Theenergy released by the burning fuel in the boiler furnace is stored (astemperature and pressure) in the steam produced. All boilers have afurnace or combustion chamber where fuel is burnt to release its energy.

Air is supplied to the boiler furnace to enable combustion of the fuel totake place. A large surface area between the combustion chamber andthe water enables the energy of combustion, in the form of heat, to betransferred to the water.


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Boiler arrangement for general cargo ships - how it works ?

Formation of marine boiler

A boiler in one form or another will be found on every type of ship. Where the main machinery is steam powered, one or more l arge watertube boilers will befitted to produce steam at very high temperatures and pressures. On a diesel main machinery vessel, a smaller (usually f iretube type) boiler will be fit ted toprovide steam for the various ship services. Even within the two basic design types, watertube and firetube, a variety of designs and variations exist.

A boiler is used to heat feed water in order to produce steam. The energy released by the burning fuel in the boiler furnace is stored (as temperature andpressure) in the steam produced. All boilers have a furnace or combustion chamber where fuel is burnt to release its energy. Air is supplied to the boilerfurnace to enable combustion of the fuel to take place. A large surface area between the combustion chamber and the water enables the energy of combustion,in the form of heat, to be transferred to the water.

A drum must be provided where steam and water can separate. There must also be a variety of fittings and controls to ensure that fuel oil, air and feedwatersupplies are matched to the demand for steam. Finally there must be a number of fittings or mountings which ensure the safe operation of the boiler.

In the steam generation process the feedwater enters the boiler where it is heated and becomes steam. The feedwater circulates from the steam drum to thewater drum and is heated in the process. Some of the feedwater passes through tubes surrounding the furnace, i.e. waterwall and floor tubes, where it is heated

and returned to the steam drum. Large-bore downcomer tubes are used to circulate feedwater between the drums. The downcomer tubes pass outside of thefurnace and join the steam and water drums.


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Fig: General cargo ship boiler arrangement


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The steam is produced in a steam drum and may be drawn off for use fromhere. It is known as 'wet' or saturated steam in this condition because it willcontain small quantities of water, Alternatively the steam may pass to asuperheater which is located within the boiler. Here steam is further heated and'dried', i.e. all traces of water are converted into steam. This superheated steamthen leaves the boiler for use in the system. The temperature of superheatedsteam will be above that of the steam in the drum. An 'attemperator', i.e. a

steam cooler, may be fitted in the system to control the superheated steamtemperature.

The hot gases produced in the furnace are used to heat the feedwater toproduce steam and also to superheat the steam from the boiler drum. The gasesthen pass over an economiser through which the feedwater passes before it

enters the boiler. The exhaust gases may also pass over an air heater whichwarms the combustion air before it enters the furnace. In this way a largeproportion of the heat energy from the hot gases is used before they areexhausted from the funnel. The arrangement is shown in Figure


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Two basically different types of boiler exist, namely thewatertube and the firetube. In the watertube the feedwater is

passed through the tubes and the hot gases pass over them. In

the firetube boiler the hot gases pass through the tubes and

the feedwater surrounds them.


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Fire tube boilers

Requirement of firetube boiler for low-pressure steamproduction

A boiler is used to heat feed water in order to produce steam. Theenergy released by the burning fuel in the boiler furnace is stored(as temperature and pressure) in the steam produced.

The firetube boiler is usually chosen for low-pressure steamproduction on vessels requiring steam for auxiliary purposes.Operation is simple and feedwater of medium quality may beemployed. The name 'tank boiler is sometimes used for firetube

boilers because of their large water capacity. The terms 'smoketube' and 'donkey boiler are also in use.


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Most firetube boilers are now supplied as a completelypackaged unit. This will include the oil burner, fuel pump,

forced-draught fan, feed pumps and automatic controls for

the system. The boiler will be fitted with all the appropriate

boiler mountings.


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Fig: Fire Tube Boiler arrangement


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A single-furnace three-pass design is shown in Figure above. Thefirst pass is through the partly corrugated furnace and into thecylindrical wetback combustion chamber. The second pass is backover the furnace through small-bore smoke tubes and then theflow divides at the front central smoke box. The third pass is

through outer smoke tubes to the gas exit at the back of the boiler.

There is no combustion chamber refractory lining other than alining to the combustion chamber access door and the primary andsecondary quart. Fully automatic controls are provided and

located in a control panel at the side of the boiler.


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Cochran boilers

The modern vertical Cochran boiler has a fully spherical furnace and is knownas the 'spheroid' . The furnace is surrounded by water and therefore requires norefractory lining. The hot gases make a single pass through the horizontal tubebank before passing away to exhaust. The use of small-bore tubes fitted withretarders ensures better heat transfer and cleaner tubes as a result of the

turbulent gas flow.

Composite boilers

A composite boiler arrangement permits steam generation either by oil firing

when necessary or by using the engine exhaust gases when the ship is at sea.Composite boilers are based on firetube boiler designs. The Cochran boiler, forexample, would have a section of the tube bank separately arranged for theengine exhaust gases to pass through and exit via their own exhaust duct.


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Water tube boilers

Why Water Tube Boilers ? http://www.brighthubengineering.com/marine-engines-

machinery/43729-types-of-marine-boilers-watertube-

boilers/
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Water tube boiler functional requirement


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A boiler is used to heat feed water in order to producesteam. The energy released by the burning fuel in the boilerfurnace is stored (as temperature and pressure) in the steamproduced.

A double evaporation boiler uses two independent systemsfor steam generation and therefore avoids any contamination

between the primary and secondary feedwater. The primarycircuit is in effect a conventional watertube boiler which

provides steam to the heating coils of a steam-to-steamgenerator, which is the secondary system. The complete

boiler is enclosed in a pressurised casing.


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In contrast to its internal construction, which includes asmall steam drum and small diameter tubes, the water tube

boileris used to generate steam having high pressure and

temperature. These small internal parts produce high volume

steam for high capacity applications.
http://www.brighthubengineering.com/marine-engines-machinery/43728-marine-boilers-a-general-overview/http://www.brighthubengineering.com/marine-engines-machinery/43728-marine-boilers-a-general-overview/


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Water tube boilers are the most widely used boilers. Thesetype has replaced many boilers, including the fire tube type,mainly because of the following reasons :

The weight of the water tube boiler is much less than any

type of boiler of equivalent size. Steam raising and steam generation process is much faster

The design is custom made and flexible to include any kind ofmodifications

It has very high efficiency than the rest of the boilers The design facilitates good natural circulation of the feed

water


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The earlier versions of water tube boiler consisted of a singledrum arrangement with headers connected using short, bent

pipes with straight tubes. The hot gases used to pass over the

tubes in only one go or a single pass.

But with the advent of bent tube design, the boilers werefitted with two drums with a an integral furnace.The boilers

are known as D shaped design or D shaped Boilers.


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The D type boilers has an arrangement of two drums at theside of the furnace and is surrounded by water tube walls .

The steam drum is at the top and the water drum is located

at the bottom of the whole system. The water wall tubes are

connected either to the top and bottom headers or to thebottom header and the steam drum. The return tubes going

to the steam drum are connected to the upper header.


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Construction of a water tube boiler

Both the drums are connected with large number of small diametertubes which carry feed water. These small diameter tubes are known asgenerating tubes because they provide the main heat transfer surfaces forthe production of steam. Water is circulated between both the drumswith the help of externally fitted Large bore downcomers. Refractorymaterial is used in the making of the furnace floor, burner wall and

behind the water walls. The refractory material acts as an insulation,preventing heat from escaping. The superheater is located away from thefurnace and in between the two boilers. The boiler is also provided witha double casing which allows the passage of combustion air to the aircontrol register surrounding the burner.

The D type boiler also has a two stage superheater - primary and

secondary, located below the generating tubes. It also has anattemperator to control the temperature of steam. This basic D typeboiler is also known as ESD (Emergency Shutdown Boiler).


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The steam to steam generator working principleand operational procedure


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The steam to steam generator

A boiler is used to heat feed water in order to produce steam. Theenergy released by the burning fuel in the boiler furnace is stored (astemperature and pressure) in the steam produced.

Steam-to-steam generators produce low-pressure saturated steam fordomestic and other services. They are used in conjunction withwatertube boilers to provide a secondary steam circuit which avoids anypossible contamination of the primary-circuit feedwater. Thearrangement may be horizontal or vertical with coils within the shellwhich heat the feedwater.

The coils are supplied with high-pressure, hightemperature steam fromthe main boiler.


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Raising Steam

Fuel Quality

Boilers are usually fired using heavy fuel oil. If it is necessary because of insufficient steam for fuelheating, to use Diesel Oil or other lower viscosity fuel a single pressure jet burner with the smallestavailable tip is to be used. If this is not available, then the smallest steam atomising or steam assistedtip can be used, provided that the steam connections are blanked off. The boiler is to revert to firingon heavy fuel oil once appropriate steam heating pressure is reached.

Purging

Should the burner fail to ignite, or flame failure occur, then it is essential that the furnace is visuallyexamined for unburned fuel and purged before any attempt is made to re-ignite the burner. If the

boiler furnace or furnaces are fitted with automatic purging systems then these must be fullyoperational. If the furnace or furnaces are not fitted with automatic purging sequence systems orthey are not operational then prior to burner ignition, and on each subsequent occasion prior to re-

igniting the burner or burners the furnace spaces are to be purged using the forced draft fans togive a minimum of five full changes of furnace air.


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Manual Firing

If manual firing has to be resorted to, then the procedure must be in accordance with the manufacturersinstructions and as agreed with the Technical Department of the relevant management office.

Firing

The procedure for firing must be in accordance with manufacturers instructions. Heating should be gradual anduniform, starting with one burner using the smallest tip available. A period of six hours should normally beallowed for raising steam, but in cases where repairs to refractory, or parts subject to pressure, have been carried

out the period should be extended to 24 hours with alternate registers used.

Flow through Superheaters

Steam flow through superheaters must be maintained at all times. In cases of emergency when steam is required atshort notice the boiler manufacturers instructions are to be adhered to.

Venting

Throughout the steam raising process, provision is to be made for venting all air from the boiler. This should bedone solely by means of a designated air release cock or, if this is not fitted, by means of the steam pressure gaugecock. Under no circumstances are the steam connections of the water level gauge glasses to be used for ventingpurposes.


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Safety guideline for boiler operations in machinery spaces onboard cargo ship


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Working with marine boilerUse of Boiler Gauge Glasses

Boiler water is to be kept within the upper and lower limits at all times. If thewater level disappears from either the top or the bottom of the glass and doesnot return immediately, then all burners are to be shut off until the water level

has been restored in the gauge glass. Any such loss of water must be recorded inthe Engine Log Book and reported to the Chief Engineer.

Whenever the water level indicated is suspect it is essential that the remotewater level indications are not used in place of the readings from the water levelgauge glass. Low pressure water level gauge glasses are to be "blown down" byan approved method for the type of gauge glass at least once per watch orwhenever the water level indication is suspect. High pressure water level gaugeglasses are to be blown through only when necessary.


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Testing of Boiler Water Controls, Regulators, Alarms and Trips.All boiler controls, regulators, alarms and trips must be tested regularly inaccordance with the applicable Planned Maintenance System and makersrecommendations. Each test is to be recorded with the signature of theEngineer Officer who conducted the test.

Boiler level alarms or trip defects are to be rectified immediately. The boilershould not normally be operated with any such safeguards inoperative unlessunder the supervision of the Chief Engineer. In this circumstance the boilermust be continuously monitored.

The appropriate Management office is to be advised of details of any defects,remedial measures taken, and confirmation of satisfactory re-tests which arealso to be recorded in the Engine Room Log Book.


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Boiler Water Tests and Treatment

Water in the boilers, steam/steam generators together withsamples from their feed water systems is to be tested daily. Testingis to be carried out in accordance with procedures laid down by

the suppliers of the water treatment systems. Completion of testsis to be recorded in Engine Room logbook and the full resultsentered on the appropriate forms and sent to the laboratory forevaluation. Test results indicating contamination or loss ofchemical reserve are to be investigated immediately.

Departures from normal operating conditions are to be recorded,and the relevant Management Office immediately advised.


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Storage and Handling of Boiler Chemicals

Attention is drawn to the spontaneous combustion properties

of certain oxygen scavenging materials such as hydrazine. Any

material (e.g. cleaning material, rags, cotton waste, sawdustetc.) contaminated with chemicals of this type, must be

washed or destroyed immediately, to avoid the risk of self

ignition.


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Blowing Down Boilers

Boilers are to be blown down at least once per week dependent

upon the frequency required to control the level of dissolved

solids contained in the boiler water. Ideally blowdown should be

carried out under light load conditions with at least one tonne

being blown down from each boiler, the actual quantity being

recorded in the ER log book and the boiler water report forms.

Blowing down is to be carried out irrespective of the salinity orchemical reserve readings. Use is also to be made of the surface

blow down valve to remove scum from the boiler.


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Boiler Maintenance at Sea

Should it become necessary to shut a boiler down for repairs

or routine maintenance, and if this results in a reduction in

speed or adversely affects operational requirements, theappropriate Management Office must be informed. Details

concerning the reason for the shutdown and the likely delay

should be advised. For main propulsion boilers, wherever

possible, routine maintenance should be carried out duringballast rather than loaded passages.


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Cleaning of Gas Side Surfaces

During cargo operations, in the interests of safety, and in

particular to avoid the possible emission of sparks, the use of

soot blowers or other devices for cleaning the gas sidesurfaces is prohibited.


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Safety Precautions during Boiler Operation, Maintenance andCleaning

During the operation, cleaning and maintenance of boilers safeworking practices are of paramount importance. Qualified

personnel are to be familiar with correct operational proceduresand manufacturers recommendations.

Where these operations involve personnel entering the gas orwater spaces, the full safety precautions outlined in the Company

Safety and Environmental Manual are to be adhered to. Inparticular, respirators, protective clothing, and low voltage lampsare to be used.


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Spark and Smoke Emission

You should be aware that under various regulations applicable to the area your vessel is in, it may be an offence toemit dark smoke. The Master should therefore request appropriate detailed information from the local agentconcerning the area emission regulations and pass the information to the Chief Engineer. Careful considerationshould be given to the location and operational circumstance of the vessel before soot blowing. Permission should

be sought from the bridge before soot blowing.

Soot blowing or cleaning of turbochargers should not be carried out when gas freeing cargo tanks, whenbunkering or transferring fuel or when working cargo alongside a terminal or during ship to ship transfer. In order

to ensure that sparks are not generated from the funnel flame arrestors and screens they must be regularlychecked and replaced when required. High back pressures can be generated if these devices become blocked.Flame screens must not be painted.

Emissions of smoke, soot and exhaust gases such as COx, NOx and SOx (Carbon, nitrogen and sulphur) isminimised by controlled running, systematic maintenance and inspection routines of machinery, boilers andfunnel. The emissions of exhaust gases contribute to pollution and environmental problems such as acidificationand global warming. We aim to focus on control and reduction of the emission of these harmful gases. Reference ismade to MARPOL Annex VI and of the Companys Safety and Environmental Procedures.

Some of the ships are equipped with funnel filters to prevent large emissions from occurring. Special care shall beexercised during port stays and when starting main and auxiliary engines and lighting boilers.


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General precautions

A notice should be displayed at each boiler setting out operating instructions. Information provided by the manufacturers of the oil-burning equipment shouldbe displayed in the boiler room.

To avoid the danger of a blowback when lighting boilers, the correct flashing up procedure should always be followed:

(i) there should be no loose oil on the furnace floor;

(ii) the oil should be at the correct temperature for the grade of oil being used; if not, the temperature of the oil must be regulated before lighting is attempted;

(iii) the furnace should be blown through with air to clear any oil vapour; (iv) the torch, specially provided for the purpose, should always be used for lighting aburner unless an adjacent burner in the same furnace is already lit; other means of ignition, such as introducing loose burning material into the furnace, shouldnot be used. An explosion may result from attempts to relight a burner from the hot brickwork of the furnace;

(v) if all is in order, the operator should stand to one side, and the lighted torch inserted and fuel turned on. Care should be taken that there is not too much oilon the torch which could drip and possibly cause a fire;

(vi) if the oil does not light immediately, the fuel supply should be turned off and the furnace ventilated by allowing air to blow through for two or threeminutes to clear any oil vapour before a second attempt to light is made. During this interval the burner should be removed and the atomizer and tip inspectedto verify that they are in good order;

(vii) if there is a total flame failure while the burner is alight, the fuel supply should be turned off.

The avenues of escape from the boiler fronts and firing spaces should be kept clear.

Where required to be fitted, the gauge glass cover should always be in place when the glass is under pressure. If a gauge glass or cover needs to be replaced orrepaired, the gauge should be shut off and drained before the cover is removed.

Documents

Steam_turbines General